Monitoring could have saved rice plants

PNS/ PhilRice — Visiting rice fields regularly may now become a habit of farmers after white stemborers (WSB) hit some areas in Mindanao from July to August.

WSB injure the rice stem causing deadheart during vegetative stage and whiteheads during reproductive stage. Deadheart is the drying of the central whorl while whiteheads are discolored panicles with empty or partially filled grains.

“Close monitoring of WSB moths and egg masses could have minimized severe damage in the field,” Frezzel Praise J. Tadle, an expert on rice pests based at PhilRice-Midsayap said.

In M’lang, North Cotabato, where WSB infestation occurred at vegetative phase, damage were reported at 350 ha while more than 500 ha were hit at the reproductive phase in Davao Del Norte. Extent of deadheart occurrences were recorded at 85.76 percent per hill while whiteheads were registered at 13.94 percent.

Tadle said regular monitoring of monthly occurrence and population of stemborers is important as it determines the right time to apply insecticide.

“Most of the early infestation is a carryover from seedbed to planting so we recommend close monitoring by using light traps,” she said.

Light trap population, Tadle noted, peaked in the fourth week of April and first week of June with less than a thousand populations. Meanwhile, high density population was noted in the first and second week of July with collected population ranging from 2,000 to 2,300 white stemborers.

Experts recommend applying systemic insecticide when 1-2 egg masses are observed in every square meter. However, when damage occurs at early tillering stage, Tadle emphasized that application is unnecessary as plants compensate by producing additional tillers.

Tadle also pointed that pesticide use is no longer effective when the larva is inside the stem. Larva is the most destructive stage in the pest’s life cycle as it feeds inside the rice stem for about 28-40 days.

Monitoring regions 11 and 12, she found that areas most affected are planted late and where asynchronous planting is predominantly practiced.

She also emphasized the use of tolerant varieties. Field trials in Midsayap show that NSIC Rc158 is more susceptible to WSB damage at vegetative phase than NSIC Rc128 and NSIC Rc122.

Application of 1 kg of carbonized rice hull (CRH) per square meter in the seedbed also reduces pest incidence. The silica content of CRH hardens the stem of the rice plant preventing the entry of WSB.

Moreover, monitoring and handpicking of the egg masses in the seedbed are important farm practices.

In terms of fertilizer application, she said that nitrogen must be applied with the right amount. Studies in the station reveal that larvae has the least population in fields applied with 60 kg of nitrogen per hectare (N/ha) than on areas applied with 90 kg and 120 kg of N/ha.

Tagle added that alternate planting of varieties every two to four cropping will delay insect pests’ adaptation and prevent build-up of insect pests.

“With the management practices I mentioned, close monitoring of WSB moths and egg masses remains the most efficient way to avoid severe damage in the field,” Tadle advised.

DA-PhilRice is a government-owned and –controlled corporation that aims at developing high-yielding and cost-reducing technologies so farmers can produce enough rice for all Filipinos.